Overview

ABO incompatibility is a reaction of the immune system that occurs if two different and not compatible blood types are mixed together.

What are the symptoms of ABO incompatibility?

The following are symptoms of transfusion reactions:

Back pain

Blood in urine

Feeling of “impending doom”

Fever

Yellow skin (jaundice)

What causes ABO incompatibility?

A, B, and O are the three major blood types. The types are based on small substances (molecules) on the surface of the blood cells. In people who have different blood types, these molecules act as immune system triggers (antigens).

Each person has a combination of two of these surface molecules. Type O lacks any molecule. The different blood types are:

Type A (AA or AO molecules)

Type B (BB or BO molecules)

Type AB

Type O

People who have one blood type form proteins (antibodies) that cause their immune system to react against other blood types. Being exposed to another type of blood can cause a reaction. This is important when a patient needs to receive blood (transfusion) or have an organ transplant. The blood types must be matched to avoid an ABO incompatibility reaction. For example:

A patient with type A blood will react against type B or type AB blood

A patient with type B blood will react against type A or type AB blood

Because type O lacks any surface molecules, type O blood does not cause an immune response. This is why type O blood cells can be given to patients of any blood type. People with type O blood are called universal donors. However, people with type O can only receive type O blood.

Since antibodies are in the liquid part of blood (plasma), both blood and plasma transfusions must be matched to avoid an immune reaction.

When to seek urgent medical care?

Call your health care provider if you have recently had a blood transfusion or transplant and you have the symptoms listed above.